Method for toolmatching and troubleshooting a plasma processing system

ABSTRACT

A method tests a plasma processing system having a chamber, an RF power source, and a matching network. An RF power signal is generated from the RF power source to the chamber without igniting any plasma within the chamber. The voltage of the RF power signal, the current of the RF power signal, and the phase of the RF power signal, received by the chamber is measured while holding other parameters affecting the chamber constant. A value representative of an impedance of the chamber is computed based on the voltage, the current, and the phase. The value is then compared with a reference value to determine any defects in the plasma processing system. The reference value is representative of the impedance of a defect-free chamber.

RELATED APPLICATION

[0001] The present application claims the benefit of U.S. ProvisionalPatent Application Serial No. 60/414,108, filed Sep. 26, 2002 in thename of inventors Armen Avoyan and Seyed Jafar Jafarian-Tehrani andcommonly assigned herewith.

FIELD OF THE INVENTION

[0002] The present invention relates to the fabrication of an electronicdevice. More particularly, the present invention relates to a method andsystem for verifying a plasma processing system.

BACKGROUND OF THE INVENTION

[0003] Various forms of processing with ionized gases, such as plasmaetching and reactive ion etching, are increasing in importanceparticularly in the area of semiconductor device manufacturing. Ofparticular interest are the devices used in the etching process.Capacitively and inductively coupled plasma etching systems may be usedin the processing and fabrication of semiconductor devices. A plasmaprocessing system typically includes a plasma reactor having a plasmachamber therein. An RF power generator supplies RF power to the plasmachamber.

[0004] As the principal driving force in plasma formation, the RFfrequency and power should be the most carefully controlled parameter.Unfortunately, this is most typically not the case. FIG. 1, for example,shows RF network 10 that produces RF power for an electronic device andfabrication reactor. In particular, for producing RF plasma generation,RF power generator 12 connects to local automated matching network 14via cable 16. From local automated matching network 14, mechanical RFconnection 18 goes to process chamber 20. Process chamber 20 includescathode 22 that affects process gas 24 within plasma sheath 26 toproduce an RF plasma.

[0005] In RF network 10, certain limitations exist. For example, RFpower generator 12, while including solid state technology, still is abulky system that consumes an undesirable about of clean room floorspace. As a result, performance of RF network 10 is often adverselyaffected by installation dependencies due to generator placement. Theobjective of local automated matching network 14 is to provide anefficient transfer of RF power from the RF power generator 12 to the RFload of plasma process gas 24 by matching the widely differentimpedances between RF power generator 12 and process chamber 20 (the RFload).

[0006] A further limitation of RF network 10 relates to process chamber20 itself. Within process chamber 20, the electronic device, such as asemiconductor wafer, is positioned and processed to achieve some desiredresult such as etch or deposition. With regard to process chamber 20,two significant limitations exist. First of all, even with knowninstallation dependencies and variability due to the local automatedmatching network 14, the RF power is primarily controlled based on ameasurement made at RF power generator 12. Furthermore, even though RFpower generator 12 for a given power level consists of three variablesof voltage, current and phase angle, known systems generally measure andcontrol RF power with the unit of watts only.

[0007] There may exist many other problems associated with the plasmaprocessing chamber. The plasma processing chamber may not produce thesame results after a long usage period because of chamber wear andpolymer deposits. Other problems such as improper hardware assembly andinadequate torque requirements may also cause the plasma processingchamber to produce inconsistent yields.

[0008] In order to preserve consistent results of the plasma processingchamber, a need exists for a fast and accurate method to verify thecorrect assembly of the chamber hardware parts and troubleshoot thechamber plasma processing system.

BRIEF DESCRIPTION OF THE INVENTION

[0009] A method tests a plasma processing system having a chamber, an RFpower source, and a matching network. An RF power signal is generatedfrom the RF power source to the chamber without igniting any plasmawithin the chamber. The voltage of the RF power signal, the current ofthe RF power signal, and the phase of the RF power signal, received bythe chamber is measured while holding other parameters affecting thechamber constant. A value representative of an impedance of the chamberis computed based on the voltage, the current, and the phase. The valueis then compared with a reference value to determine any defects in theplasma processing system. The reference value is representative of theimpedance of a defect-free chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated into andconstitute a part of this specification, illustrate one or moreembodiments of the present invention and, together with the detaileddescription, serve to explain the principles and implementations of theinvention.

[0011] In the drawings:

[0012]FIG. 1 is a diagram schematically illustrating a conventional RFnetwork for establishing a plasma process environment within a plasmaetching device.

[0013]FIG. 2 is a diagram schematically illustrating a system forverifying a plasma processing system in accordance with one embodimentof the present invention.

[0014]FIG. 3 is a block diagram of a computer system suitable forimplementing aspects of the present invention.

[0015]FIG. 4 is a flow diagram schematically illustrating a method forverifying a plasma processing system in accordance with one embodimentof the present invention.

[0016]FIG. 5 is a flow diagram schematically illustrating a method fortoolmatching a plasma processing system in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION

[0017] Embodiments of the present invention are described herein in thecontext of a plasma processing system. Those of ordinary skill in theart will realize that the following detailed description of the presentinvention is illustrative only and is not intended to be in any waylimiting. Other embodiments of the present invention will readilysuggest themselves to such skilled persons having the benefit of thisdisclosure. Reference will now be made in detail to implementations ofthe present invention as illustrated in the accompanying drawings. Thesame reference indicators will be used throughout the drawings and thefollowing detailed description to refer to the same or like parts.

[0018] In the interest of clarity, not all of the routine features ofthe implementations described herein are shown and described. It will,of course, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application-and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

[0019] In accordance with one embodiment of the present invention, thecomponents, process steps, and/or data structures may be implementedusing various types of operating systems (OS), computing platforms,firmware, computer programs, computer languages, and/or general-purposemachines. The method can be run as a programmed process running onprocessing circuitry. The processing circuitry can take the form ofnumerous combinations of processors and operating systems, or astand-alone device. The process can be implemented as instructionsexecuted by such hardware, hardware alone, or any combination thereof.The software may be stored on a program storage device readable by amachine.

[0020] In addition, those of ordinary skill in the art will recognizethat devices of a less general purpose nature, such as hardwireddevices, field programmable logic devices (FPLDs), including fieldprogrammable gate arrays (FPGAs) and complex programmable logic devices(CPLDs), application specific integrated circuits (ASICs), or the like,may also be used without departing from the scope and spirit of theinventive concepts disclosed herein.

[0021] In accordance with one embodiment of the present invention, themethod may be implemented on a data processing computer such as apersonal computer, workstation computer, mainframe computer, or highperformance server running an OS such as Solaris® available from SunMicrosystems, Inc. of Palo Alto, Calif., Microsoft® Windows® XP andWindows® 2000, available form Microsoft Corporation of Redmond, Wash.,or various versions of the Unix operating system such as Linux availablefrom a number of vendors. The method may also be implemented on amultiple-processor system, or in a computing environment includingvarious peripherals such as input devices, output devices, displays,pointing devices, memories, storage devices, media interfaces fortransferring data to and from the processor(s), and the like. Inaddition, such a computer system or computing environment may benetworked locally, or over the Internet.

[0022]FIG. 2 is a diagram schematically illustrating a system 200 forverifying a plasma processing system in accordance with one embodimentof the present invention. In the system 200, Radio Frequency (RF) powergenerator 202 supplies RF power to a bottom electrode 204 disposedwithin a plasma processing chamber 206. RF current may flow between thebottom electrode 204 and the top grounded electrode 205. In accordancewith one embodiment of the present invention, the RF power generator 202may be a dual frequency generator generating, for example, 2 Mhz and 27MHz. Those of ordinary skill in the art will appreciate that the aboveexample shown are not intended to be limiting and that other frequenciesmay be used without departing from the inventive concepts hereindisclosed.

[0023] A matching network 208 connects the RF power generator 202 to thechamber 206. To provide an efficient transfer of RF power from the RFpower generator 202 to the chamber 206 (the RF load), the matchingnetwork 208 matches the impedance between the RF power generator 202 andthe chamber 206. Those of ordinary skills in the art will recognize thatthere exist a wide variety of designs for matching network 210, all ofwhich operate by tuning to a minimum reflected power.

[0024] A sensor 210 is coupled to the system 200 at the input of thechamber 206, between the chamber 206 and the matching network 208. Thesensor 210 measures the voltage, current, and phase angle of the RFpower signal received by the chamber 206. In accordance with oneembodiment of the present invention, the sensor 210 may be, for example,a Voltage/Current Probe (VI Probe) or a Network Analyzer. Those ofordinary skills in the art will recognize that many varieties ofvoltage, current, and phase angle sensors may be applied to the presentinvention.

[0025] A computer system 212 receives the measured data from the sensor210 (voltage, current, and phase angle). The computer system 212 allowsa user to verify whether the plasma processing system is free of anydefects and whether the chamber hardware parts are assembled correctlyby analyzing the received data. The algorithm within the computer system212 is further discussed below the flow diagram of FIG. 4. FIG. 3depicts a block diagram of a computer system 300 suitable forimplementing aspects of the present invention. As shown in FIG. 3,computer system 300 includes a bus 302 which interconnects majorsubsystems such as a central processor 304, a system memory 306(typically RAM), an input/output (I/O) controller 308, an externaldevice such as a display screen 310 via display adapter 312, serialports 314 and 316, a keyboard 318, a fixed disk drive 320, a floppy diskdrive 322 operative to receive a floppy disk 324, and a CD-ROM player326 operative to receive a CD-ROM 328. The system memory 306 may containthe algorithm described in FIG. 4. Many other devices can be connected,such as a pointing device 330 (e.g., a mouse) connected via serial port314 and a modem 332 connected via serial port 316. Modem 332 may providea direct connection to a remote server via a telephone link or to theInternet via a POP (point of presence). Alternatively, a networkinterface adapter 334 may be used to interface to a local or wide areanetwork using any network interface system known to those skilled in theart (e.g., Ethernet, xDSL, AppleTalk™).

[0026] Many other devices or subsystems (not shown) may be connected ina similar manner. Also, it is not necessary for all of the devices shownin FIG. 3 to be present to practice the present invention, as discussedbelow. Furthermore, the devices and subsystems may be interconnected indifferent ways from that shown in FIG. 3. The operation of a computersystem such as that shown in FIG. 3 is readily known in the art and isnot discussed in detail in this application, so as not to overcomplicatethe present discussion. Code to implement the present invention may beoperably disposed in system memory 306 or stored on storage media suchas fixed disk 320, floppy disk 324 or CD-ROM 328.

[0027]FIG. 4 is a flow diagram schematically illustrating a method fortroubleshooting a plasma processing system in accordance with oneembodiment of the present invention. Beginning at 402, a vacuum iscreated in the chamber 206 with a pressure of about 0 mTorr. The chamber206 may be a “clean” chamber without any wafer to be processed or gassesflowing. At 404, an RF power signal is being generated in the chamberwith no gasses flowing. For example, a low power, such as about 10 Wattsor less, at 2 Mhz or 27 Mhz may be generated through the chamber 206without igniting any plasma. At 406, sensor 210 measures the voltage,current, and phase angle of the RF power signal received at theplasma-less chamber 206. At 408, the computer system 212 receives andrecords the measured voltage, current, and phase angle of the RF powersignal. The computer system 212 computes the chamber impedance from themeasured data.

[0028] Those of ordinary skills in the art will recognize that theimpedance of the chamber is a complex quantity related to theinteraction between the AC current from the RF power generator 202(forward power) and resistance and reactance (chamber parts). Thefollowing equations illustrates the above relationship:

Z=R+jX  Equation 1

R=|Z| cos θ  Equation 2

X=|Z| sin θ  Equation 3

|Z|=V/I

[0029] Where Z is the impedance of the chamber, R is the resistance, Xis the reactance, θ is the phase angle, V is the measured voltage, and Iis the measured current.

[0030] The chamber impedance may be affected by many factors such as:the gas pressure, the gas type, the RF power, the wall conditions, thegas pressure, the RF grounding, the wafer type, the wafer placement, andthe power coupling. Thus, if any changes occur in the RF load, such asthe polymerization of the chamber wall or the wearing away ofanodization coatings on various process chamber components, the voltageand current will change, and thus the impedance of the chamber.

[0031] Because the chamber 206 is set at vacuum, the phase angle θ ofthe RF power signal through the vacuum chamber is about 90°. Because thephase angle θ is about 90°, the resistance R is about zero. Thus, theimpedance of the chamber is mostly reactance. The computed value may berepresentative of the absolute value of the impedance.

[0032] At 410, the computer system compares the computed chamberimpedance with an impedance baseline to determine whether any defectsexist. The impedance baseline is the mean impedance of plasma processingchambers of the same type in a vacuum at the time of manufacturing. Forillustration purposes, the mean impedance of a plasma-less chamber maybe, for example, 15Ω. If the measured impedance of a plasma-less chamberof the same type is off by more than at least about 10% of 15Ω, forexample, 19Ω, possible defects may exist. In that case, at 412, thechamber needs to be checked for deficiencies. Potential defects mayinclude but are not limited to the following: improper hardwareassembly, inadequate torque requirements, substandard parts used,missing hardware parts, chamber wear and arcing, polymer deposits. Afteridentifying and fixing the potential problem at 414, the troubleshootingprocess may be reiterated at 402 to verify the system.

[0033] Toolmatching may be necessary to ensure that all plasma chambersproduced are free of defects. One may be able to identify any defectiveplasma chamber by comparing the chamber impedance of all processingchambers of the same model, type, or design. FIG. 5 is a flow diagramschematically illustrating a method for toolmatching a plasma processingsystem in accordance with one embodiment of the present invention.Beginning at 502, a vacuum is created in each chamber 206 with apressure of, for example, about 0 mTorr. Each chamber 206 may be a“clean” chamber without any wafer to be processed or gasses flowing. At504, a RF power signal is being generated in each chamber with no gassesflowing through each chamber, and thus no plasma. For example, a lowpower, such as about 10 Watts or less, at 2 Mhz or 27 Mhz, may begenerated through each chamber 206 without igniting any plasma. At 506,each chamber sensor 210 measures the voltage, current, and phase angleof the RF power signal received at each plasma-less chamber 206. At 508,each chamber computer system 212 receives and records the measuredvoltage, current, and phase angle of the RF power signal. Each chambercomputer system 212 computes the chamber impedance from the measureddata.

[0034] Because the chamber 206 is set at a vacuum, the phase angle θ ofthe RF power signal through the vacuum chamber is about 90°. Because thephase angle θ is about 90°, the resistance R is about zero. Thus, theimpedance of the chamber is mostly reactance. The computed value may berepresentative of the absolute value of the impedance.

[0035] At 510, the computer system compares the impedance of eachchamber to determine whether any defects exist. For illustrationpurposes, the computed impedance of several chambers of the same typewithout any plasma with an RF power signal of 27 Mhz maybe 15.8Ω, 19.2Ω,14.9Ω, 16.2Ω, 15.9Ω. If the computed impedance of a chamber is off bymore than at least about 10% of the median computed impedance, possibledefects may exist. In the above illustration, the chamber with acomputed impedance of 19.2Ωneeds to be checked for possible defects. Inthat case, at 512, the above chamber needs to be checked for possibledeficiencies. Potential defects may include but are not limited to thefollowing: improper hardware assembly, inadequate torque requirements,substandard parts used, missing hardware parts, chamber wear and arcing,polymer deposits. After identifying and fixing the potential problem at514, the toolmatching process may be reiterated at 502 to verify thatall chambers are free of defects.

[0036] While embodiments and applications of this invention have beenshown and described, it would be apparent to those skilled in the arthaving the benefit of this disclosure that many more modifications thanmentioned above are possible without departing from the inventiveconcepts herein. The invention, therefore, is not to be restrictedexcept in the spirit of the appended claims.

What is claimed is:
 1. A method for testing a plasma processing systemhaving a chamber, an RF power source, and a matching network, the methodcomprising: generating an RF power signal from the RF power source tothe chamber without igniting any plasma within the chamber; measuring avoltage of said RF power signal, a current of said RF power signal, anda phase of said RF power signal, received by the chamber while holdingother parameters affecting the chamber constant; computing a valuerepresentative of an impedance of the chamber based on said voltage,said current, and said phase; and comparing said value with a referencevalue to determine any defects in the plasma processing system, saidreference value representative of the impedance of a defect-freechamber.
 2. The method of claim 1 further comprising: inspecting theplasma processing system when said value is not within at least about10% of said reference value.
 3. The method of claim 1 wherein said RFpower signal includes a high frequency power.
 4. The method of claim 1wherein said RF power signal includes a low frequency power.
 5. Themethod of claim 1 wherein said generating further comprises: matchingthe impedance of said RF power signal with the impedance of the chamber.6. A method for toolmatching a plurality of plasma processing chambers,the method comprising: generating a RF power signal for each chamberwithout igniting any plasma within each chamber; measuring a voltage ofsaid RF power signal, a current of said RF power signal, and a phase ofsaid RF power signal, received by each chamber while holding otherparameters affecting the chamber constant; computing a valuerepresentative of an impedance for each chamber based on said voltage,said current, and said phase; and comparing said value for each chamberwith other chambers.
 7. The method of claim 6 further comprising:isolating a plasma processing chamber when a value of a chamber is offby at least about 10% from the mean value of the other chambers.
 8. Themethod of claim 6 wherein said power includes a high frequency power. 9.The method of claim 6 wherein said power includes a low frequency power.10. The method of claim 6 wherein said generating further comprises:matching the impedance of said RF power signal with said impedance ofeach chamber.
 11. An apparatus for testing a plasma processing systemhaving a plasmaless chamber, an RF power source generating an RF powersignal, and a matching network, the apparatus comprising: a sensorcoupled to the plasmaless chamber, said sensor measuring a voltage, acurrent, and a phase angle of the RF power signal received at theplasmaless chamber while holding other parameters affecting the chamberconstant; and a computer system coupled to said sensor, said computersystem computing a value representative of an impedance of the chamberbased on said voltage, said current, and said phase, and comparing saidvalue with a reference value to determine any defects in the plasmaprocessing system, said reference value representative of the impedanceof a defect-free chamber.
 12. The apparatus of claim 11 wherein saidcomputer system issues a warning when said value is not within at leastabout 10% of said reference value.
 13. The apparatus of claim 11 whereinsaid RF power signal includes a high frequency power.
 14. The apparatusof claim 11 wherein said RF power signal includes a low frequency power.15. An apparatus for testing a plasma processing system having achamber, an RF power source, and a matching network, the apparatuscomprising: means for generating an RF power signal from the RF powersource to the chamber without igniting any plasma within the chamber;means for measuring a voltage of said RF power signal, a current of saidRF power signal, and a phase of said RF power signal, received by thechamber while holding other parameters affecting the chamber constant;means for computing a value representative of an impedance of thechamber based on said voltage, said current, and said phase; and meansfor comparing said value with a reference value to determine any defectsin the plasma processing system, said reference value representative ofthe impedance of a defect-free chamber.
 16. An apparatus fortoolmatching a plurality of plasma processing chambers, the apparatuscomprising: means for generating a RF power signal for each chamberwithout igniting any plasma within each chamber; means for measuring avoltage of said RF power signal, a current of said RF power signal, anda phase of said RF power signal, received by each chamber while holdingother parameters affecting the chamber constant; means for computing avalue representative of an impedance for each chamber based on saidvoltage, said current, and said phase; and means for comparing saidvalue for each chamber with other chambers.
 17. A program storage devicereadable by a machine, tangibly embodying a program of instructionsexecutable by the machine to perform a method for testing a plasmaprocessing system having a chamber, an RF power source, and a matchingnetwork, the method comprising: generating an RF power signal from theRF power source to the chamber without igniting any plasma within thechamber; measuring a voltage of said RF power signal, a current of saidRF power signal, and a phase of said RF power signal, received by thechamber while holding other parameters affecting the chamber constant;computing a value representative of an impedance of the chamber based onsaid voltage, said current, and said phase; and comparing said valuewith a reference value to determine any defects in the plasma processingsystem, said reference value representative of the impedance of adefect-free chamber.
 18. A program storage device readable by a machine,tangibly embodying a program of instructions executable by the machineto perform a method for toolmatching a plurality of plasma processingchambers, the method comprising: generating a RF power signal for eachchamber without igniting any plasma within each chamber; measuring avoltage of said RF power signal, a current of said RF power signal, anda phase of said RF power signal, received by each chamber while holdingother parameters affecting the chamber constant; computing a valuerepresentative of an impedance for each chamber based on said voltage,said current, and said phase; and comparing said value for each chamberwith other chambers.